Device and method for cutting an assembly

ABSTRACT

A method is presented for cutting an assembly that includes two layers of material having a first surface and a second surface. The method includes providing a weakened interface between the two layers that defines an interface ring about the periphery of the assembly, providing a high-pressure zone at the interface ring, and providing at least one controllable low-pressure zone in the vicinity of at least one of the first surface and the second surface. The technique also includes supplying the high-pressure zone with a controllable high-pressure force, and attacking the interface ring with at least one mechanical force in combination with the high-pressure force to cut the assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/886,436filed Jul. 6, 2004, now U.S. Pat. No. 7,232,738 which is a continuationof International application no. PCT/FR02/04594 filed Dec. 31, 2002, theentire contents of each of which are expressly incorporated herein byreference thereto.

BACKGROUND ART

The present invention relates generally to preparing substrates forelectronics, optics or optoelectronics. More specifically, the inventionrelates to a method for precisely cutting an assembly formed of twolayers of material that has two principal surfaces. The method includesproviding a weakened interface between the two layers, wherein theinterface defines an interface ring at the periphery of the assembly. Afirst high-pressure zone is provided whose border includes at least onepart of the interface ring, and at least one second low-pressure zone isformed whose pressure is controlled relative to one part at least of aprincipal surface of the assembly. The high-pressure zone is suppliedwith a fluid, whose pressure is controlled.

For the purposes of this text, the term “cutting” is understood to meanthe operation of dividing a single element or assembly into twophysically separate parts wherein the parts do not combine again.

Methods for cutting two layers of material of an assembly arewell-known, for example, as disclosed in International Application No.WO 01/04933. That document also describes a device for implementing themethod. In particular, this document describes the production of atleast one cavity in the interface zone, the cavity then being used forinitiating the cutting of the two layers defined by the interface. Alimitation of the disclosure of this document is that it only enablescutting of layers that have been previously bonded together, so that theweakened interface is necessarily a bonding interface. It would beadvantageous to be able to implement a method of this type for cuttinglayers separated by any type of weakened interface. It would thus beadvantageous to be able to implement a method of the aforesaid type, forexample, for cutting layers separated by a weakened interface that hasbeen defined by implantation of elements such as ions or atoms in asubstrate of material (the two layers being thus produced using the samematerial).

One way of defining a weakened interface in a substrate of the type usedfor electronics, optics, or optoelectronics includes implanting elementssuch as hydrogen ions in the substrate mass using a controlledimplantation energy to precisely define the depth of implantation of theelements. One such substrate (called a ‘wafer’ according to thegenerally accepted terminology) can be, for instance, a semiconductormaterial such as silicon.

It is also possible to produce a weakened interface by using any otherknown method, for example, by constructing an intermediate zone ofporous material between two zones of dense material. For example, byusing a layer of oxide embedded in a substrate (a silicon-on-insulator(SOI) type substrate, for example). The bonding of the two layers isthus only one particular way of creating a weakened interface betweentwo layers.

The present invention seeks to implement a method of the aforesaid typefor cutting an assembly at a weakened interface that has been formed byone of the hereinbefore described means, or by any other known method.

It is noted that that other methods are known that enable cutting oflayers separated by a weakened interface created by implantation ofatomic particles. An example of one such method can be found in U.S.Pat. No. 6,221,740. But that method does not provide the specificadvantages of the type of method described in International ApplicationNo. WO 01/04933. In particular, the method does not teach how toprecisely control the pressure in the two different zones (correspondingto the high-pressure zone and the low-pressure zone mentioned above).Such control is important for performing the cutting operations withprecision and for avoiding the risks of degrading the wafers, which arefragile and which are expected to have an extremely high surface qualityafter cutting. The device described in U.S. Pat. No. 6,221,740 thus doesnot enable one to control the pressure in one single zone of highpressure, which is adjacent to at least one part of the interface ring.And it must be noted that even this control cannot be carried out in aprecise manner due to the significant risk of leakage at the interfacering (a certain tightness being provided by an O-ring seal positionedrelative to the interface ring), although as stated in U.S. Pat. No.6,221,740 (see col. 4, lines 21-22 and lines 34-36) this tightness isrelative.

Furthermore, U.S. Pat. No. 6,221,740 does not have the advantageousstructure type described in International Application No. WO 01/04933,which not only enables defining at least one high-pressure zone and onelow-pressure zone in which the pressure can be precisely controlled, butmoreover enables the assembly to be cut to deform freely when being cut(namely owing to the absence of contact on a significant portion of theprincipal surfaces of the assembly). Thus, the structures of the devicesof International Application No. WO 01/04933 and U.S. Pat. No. 6,221,740exhibit fundamental differences that correspond to fundamentalfunctional differences.

It would thus be advantageous to preserve the advantages of the methodof International Application No. WO 01/04933 (including controlling boththe high and low pressure to precisely control the loads applied to theassembly as well as generally allowing the assembly to deform freelyduring cutting), wherein these advantages are absent in theconfiguration described by U.S. Pat. No. 6,221,740. It would also bebeneficial to enable efficient cutting at a weakened interface thatwould be produced by any means (by implantation, for example), which isnot suggested in the method and device of International Application No.WO 01/04933, which is strictly limited to cutting a weakened interfacecorresponding to a bonding interface.

SUMMARY OF THE INVENTION

A method is presented for cutting an assembly that includes two layersof material having a first surface and a second surface. The methodincludes providing a weakened interface between the two layers thatdefines an interface ring about the periphery of the assembly, providinga high-pressure zone at the interface ring, and providing at least onecontrollable low-pressure zone in the vicinity of at least one of thefirst surface and the second surface. The technique also includessupplying the high-pressure zone with a controllable high-pressureforce, and attacking the interface ring with at least one mechanicalforce in combination with the high-pressure force to cut the assembly.The method provides high-precision cutting of the two layers.

Advantageously, the weakened zone is provided by at least one ofimplanting atomic species and forming a thin porous layer between thetwo layers of material. The high-pressure force includes at least one ofa pressurized fluid and a pressurized gas. In an implementation, theassembly is placed in a receptacle, wherein the high-pressure zone andeach low-pressure zone are defined by O-rings that cooperate with theassembly. Advantageously, the method includes controlling the pressureto progressively increase in the high-pressure zone. A control loop maybe provided to increase the pressure as a function of the progress of aseparation front that is created when cutting.

In a variation, the method includes establishing a low-pressure zonerelative to both the first and second surfaces of the assembly. Thepressures of the two low-pressure zones may advantageously be separatelyand differently controlled. In a beneficial embodiment, the at least onemechanical force comprises at least one blade. An independenthigh-pressure supply may advantageously be associated with each blade toattack the assembly, and a high pressure zone may be established by eachblade which includes a high-pressure supply. In a preferred embodiment,at least one of a traction force and a shearing force is applied to thefirst and second surfaces of the assembly.

Another aspect of the invention is a device for cutting an assemblyhaving two layers of material and a weakened interface therebetween,wherein the weakened interface defines an interface ring about theperiphery of the assembly. This devices comprises a housing adapted foraccepting the assembly; at least one blade for attacking the assembly atthe interface ring; and at least one further element that cooperateswith the blade and interface ring to facilitate cutting of the assembly.

The further element may be at least one seal element for establishing ahigh-pressure zone between the housing and the assembly at the level ofthe interface ring, and for establishing a low-pressure zone at asurface of the assembly. Preferably, a second seal element is providedfor defining the high pressure zone between the housing and theassembly, and for establishing a second low-pressure zone at a secondsurface of the assembly, wherein cutting is facilitated by controllingthe pressure in at least one of the high pressure and the low pressurezones.

Alternatively, the further element may be at least one gripper forapplying a complementary mechanical action on at least one surface ofthe assembly. In this embodiment, the further element further comprisesat least one seal element for establishing a high-pressure zone betweenthe at least one blade and the interface ring.

In an implementation, the at least one seal element of the device is anO-ring. Advantageously, the device further includes an independenthigh-pressure supply for each blade of the device. In an embodiment, atleast one blade comprises an internal supply conduit for directing afluid or a gas under high-pressure. The device may also include acontrol loop for controlling the increase of high pressure as a functionof the progress of a separation front created during cutting. In abeneficial implementation, the device includes a second seal element fordefining the high pressure zone between the housing and the assembly,and for establishing a second low-pressure zone at a second surface ofthe assembly, wherein cutting is facilitated by controlling the pressurein at least one of the high pressure and the low pressure zones. Thedevice may also advantageously include at least one gripper for applyinga complementary mechanical action on at least one of two surfaces of theassembly. The complementary mechanical action includes at least one of atraction force perpendicular to the surfaces of the assembly and ashearing force oriented in the plane of the weakened interface.

In another aspect according to the invention, provided is a device forcutting an assembly having two layers of material having a weakenedinterface therebetween, wherein the weakened interface defines aninterface ring about the periphery of the assembly. The device includesat least one blade, at least one seal element and at least one gripper.The at least one blade is used to attack the assembly at the interfacering, the blade including an internal supply conduit for supplying atleast one of a fluid or a gas under high pressure. The at least one sealelement establishes a high-pressure zone between the at least one bladeand the interface ring, and the at least one gripper applies acomplementary mechanical action on at least one surface of the assembly.

In an advantageous implementation, the at least one seal element is anO-ring. The device may also include an independent high-pressure supplyfor each blade, and may include a control loop for controlling theincrease of high pressure as a function of the progress of a separationfront created during cutting. The complementary mechanical actionadvantageously includes at least one of a traction force perpendicularto the surfaces of the assembly and a shearing force oriented in theplane of the weakened interface.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, purposes and advantages of the invention will becomeclear after reading the following detailed description with reference tothe attached drawings, in which:

FIG. 1 a is a simplified schematic side view representation of a firstembodiment of a device according to the invention that includes a blade;

FIG. 1 b is a similar view of the device of FIG. 1 a, wherein the bladehas begun cutting the assembly;

FIG. 1 c is a schematic top view of the device of FIG. 1 a, wherein theblade of the device is in a position corresponding to that of FIG. 1 b;

FIG. 2 a is a simplified schematic side view representation of a devicecorresponding to a second alternative embodiment according to theinvention; and

FIG. 2 b is a schematic top view of the device shown in FIG. 2 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By way of introduction to the following description of differentalternative embodiments of the invention, it should be noted that theexamples described below represent cutting an assembly 10 that includestwo layers of material separated by a weakened interface. The two layersare arranged on either side of the weakened interface and can be made ofthe same material or of different materials. The weakened interface canbe produced by any known method. In particular, the weakened interfacecan be produced by implanting elements as hereinbefore mentioned, oreven by any other known means (for example, by forming a thin porouslayer between the two layers which then corresponds to the weakenedinterface).

It is also noted that, although the figures illustrating the assemblyshow two relatively thick layers, in reality these layers can beextremely thin. In particular, in one preferred application of theinvention, the assembly can be a Silicon-On-Insulator (SOI) substratetype (or, more generally, a Silicon-On-Anything (SOA) assembly,according to generally accepted terminology for such substrates, or evenan—Anything-On-Anything (AOA) type substrate). Hereinafter, the assembly10 may also be referred to as a “wafer.”

FIG. 1 a illustrates a wafer 10 comprising two layers 10 a and 10 b thatare separated by a weakened layer or weakened interface 11. A firstprincipal surface 10 a 1 of the wafer 10 is located on the surface ofthe first layer 10 a opposite the weakened interface 11. A secondprincipal surface 10 b 1 is located on the surface of the second layer10 b opposite the other side of the weakened interface 11. The wafer 10thus includes two layers 10 a and 10 b separated by a weakened interface11, wherein the two layers define the two principal surfaces 10 a 1 and10 b 1 at their respective external surfaces. The weakened interface 11defines a circular line at the periphery of the wafer that shall bereferred to as the “interface ring”.

The wafer 10 typically has a circular shape, the two layers 10 a and 10b thus take the form of two superimposed disks joined by the weakenedinterface 11. As mentioned above, the weakened interface can be producedby any known method. It should be noted that the wafer 10 might beprepared by undergoing a specific treatment to facilitate cutting alongthe weakened interface 11. One such preparation treatment, for example,may include subjecting the wafer 10 to a high-temperature annealing typethermal treatment. More particularly, if the weakened interface isproduced by implantation, such a thermal treatment preparation canenable “over-weakening” of the interface 11, it being understood thatthe thermal budget utilized during such a treatment step must remainbelow the thermal budget required to completely cleave or detach the twolayers 10 a and 10 b. In this manner, cutting (that is, the operationenabling definitive separation of the two sections 10 a and 10 b fromeach other) is facilitated.

The wafer is placed in a receptacle or housing 20 that enables at leastone high-pressure zone and one low-pressure zone to be defined. Morespecifically, the housing 20 comprises two O-rings 20 a and 20 b thatare tightly or securely arranged against the respective principalsurfaces 10 a 1 and 10 b 1 of the wafer. Each O-ring is thusconcentrically arranged relative to the wafer. Each O-ring 20 a, 20 b isalso in tight contact with the wall of the housing 20. Such aconfiguration thus produces a peripheral zone 21 that encompasses thewafer 10 at its lateral wall and includes the zone corresponding to theinterface ring, and two zones 22 a and 22 b that are delimited by therespective O-rings 20 a and 20 b and which are arranged to include thetwo principal surfaces of the wafer, inside the housing or receptacle20.

In FIG. 1 a, it is important to note the presence of a fluid inlet 210for supplying the zone 21 with a fluid under controlled pressure (forexample, by way of a valve 211). The zone 21 is the “high-pressure” zonebecause the controlled pressure of the fluid being supplied to the zone21 is greater than the pressure that exists in the zones 22 a and 22 b.In fact, the pressure that exists in the two zones 22 a and 22 b canalso be controlled by any known means. It should be noted that the fluidthat fills the zones 22 a and 22 b can simply be air or even a specificgas mixture or, generally, any fluid or mixture of fluids adapted forcontrolling the pressure on the external surfaces of the wafer.Likewise, the fluid arriving via the supply 210 can be any fluid adaptedto provide high pressure in the zone 21 which aids, as will be shown, inthe cutting of the two layers of the wafer. It is noted that the fluidused to establish the high pressure zone may have chemical propertiesenabling it to attack the interface 11 and thus facilitate cutting (forexample, if an oxide layer is to be cut, a liquid or gaseous HF fluidcould be used).

In the embodiment represented in FIGS. 1 a to 1 c, the pressure of zones22 a and 22 b is simply controlled by means of two vents 21 a and 21 bthat allow air (or generally, a fluid) contained in these respective twozones to freely communicate with the ambient atmosphere surrounding thehousing 20. In this case, the “low pressure” of zones 22 a and 22 b iscontrolled to correspond to the surrounding pressure. In the case of areceptacle placed in air at atmospheric pressure, the low pressure isthus controlled in a manner so as to be equal to the atmosphericpressure.

It is also important to note (particularly in FIGS. 1 a and 1 b) thepresence of a blade 30 that is arranged in the high-pressure zone 21.The blade 30 is placed in the axis of the weakened interface 11, theleading edge of the blade being arranged at the level of the interfacering corresponding to the weakened interface 11. In addition, the blade30 is mounted on specific control means that enables the regulation ofits displacement in the plane of the weakened interface 11 (thesespecific control means are not shown but can be of any known type).

The O-rings 20 a and 20 b can be replaced by seals that have anothershape or by any specific means that enable the establishment of a tightseal between the zone 21 and the zones 22 a and 22 b. Further, it ispossible according to the invention to define only one zone 22 a or 22 bwith regard to only one of the two principal surfaces of the wafer. Inthis case, the other face of the wafer can be enclosed by thehigh-pressure zone 21. In particular, the configuration of thelow-pressure zones could be adapted to favor deformation of one of thetwo layers 10 a or 10 b of the wafer, which may be determined as afunction of the respective materials comprising the two layers. In fact,in the case of the two layers of two different materials, it is possibleand it may be desirable to encourage deformation of one of the twolayers during cutting. In such a case, a low-pressure zone relative tothe principal surface of the wafer that corresponds to the desired layercould be formed. It is also be possible to control the “low pressures”of the two zones 22 aand 22 b separately and differently to apply apressure differential between the two layers, and thus provide a greaterload on one of the layers. The pressure of the fluid supplied in thehigh-pressure zone 21 can also be controlled to progressively establisha high-pressure in this zone. In this case, it would be possible todefine any control sequence to produce such a pressure increase more orless rapidly and/or more or less continuously.

Referring to FIGS. 1 b and 1 c, in conjunction with establishing a highpressure P1 in the zone 21 (pressure P1 being greater than pressure P0existing in the zones 22 a and 22 b), movement of the blade 30 iscontrolled so that the leading edge of the blade attacks the wafer atthe level of its interface ring. The interface ring corresponds to theintersection of the weakened interface 11 and the periphery of the wafer10. Also, while the two layers of the wafer 10 are shown have bevelededges in the figures, it is also possible that these edges are more orless sharply defined. The position of the leading edge of the blade,which is perpendicular to the principal surfaces of the wafer, is aimedprecisely so that when it is displaced the leading edge of the bladeattacks the wafer at the interface ring. However, it is also possible tocombine the blade 30 with means that allow a certain amount of freedomin the vertical direction to enable self-adjustment of the verticalposition of the leading edge of the blade as it comes into contact withthe interface ring. One such self-adjustment can be implemented when theinterface ring is defined by beveled edges of the layers 10 a and 10 b.In this case, the interface ring is located between the beveled edgeswhich will guide the leading edge of the blade towards the weakenedinterface 11 at the time of the attack.

FIG. 1 b shows the device according to the invention wherein the blade30 has attacked the weakened interface 11 and has started to separatethe two layers 10 a and 10 b. It should be noted that the differentelements shown in the figures are not drawn to scale but are drawn forease of understanding only, and thus do not represent reality. Forexample, when the blade 30 attacks an SOI structure, the two layers 10 aand 10 b are separated only by the width of the blade, which can be onthe order of a millimeter. In addition, the deformation of the layers 10a and 10 bas shown in FIG. 1 b is greatly exaggerated. In any case,penetration of the blade between the two layers 10 a and 10 b enablesthe creation and propagation of a separation front between the twolayers, and such a separation front 100 is schematically shown in FIG. 1c. In the field of cutting SOI structures, for example, it is known thatit is possible to observe such separation fronts (for example, bymeasurement of the reflection and/or transmission of a light ray such asan infrared light ray illuminating the wafer as it is being cut).

The blade 30 attacks the wafer only on one small portion of itsperiphery. In this respect, the contour of the blade may correspond to aprojecting geometry to attack the wafer on one small portion of itsperiphery as shown in the top view of FIG. 1 b. It is also possible todefine a different geometry for the blade 30, for example, a concave“crescent” profile when viewed from above (corresponding to the view inFIG. 1 c). In this case, the leading edge of the blade would thenco-operate with an entire angular sector of the periphery of the wafer.In any case, when the blade 30 attacks the wafer and induces separationbetween the two layers 10 a and 10 b(the O-rings 20 a and 20 b beingdisposed in a recess from the periphery of the wafer 10 in such afashion that such initial separation is possible), the fluid under highpressure in zone 21 can penetrate (including on the sides of the blade)between the two layers 10 a and 10 b on the sides and ahead of the blade30. In this manner, a zone 1000 is created between the two layers 10 aand 10 b ahead of the blade 30, in which the pressure is substantiallyequal to P1.

Once the blade has progressed sufficiently between the two layers 10 aand 10 b so that the zone 1000 is parallel to the principal surfaces ofthe wafer that are enclosed by the seals 20 a and 20 b, at least onepart of the layers 10 a and 10 b is subjected to a separating stressfrom the other layer as a result of the pressure differential (P1-P0).The pressure differential thus facilitates the separation of the twolayers 10 a and 10 b. It is noted in this respect that the configurationof the device according to the invention makes it possible to free thetwo layers 10 a and 10 b to deform by vertically separating them fromeach other (contrary to that obtained using the configuration describedin U.S. Pat. No. 6,221,740). Thus, the combined action of the blade andthe stress generated by the pressure differential (P1-P0) makes itpossible to cut the wafer under optimal conditions.

In a preferred embodiment, the elasticity of the seals 20 a and 20 b isdefined to allow a certain separation of the layers 10 a and 10 b fromeach other to enable the completion of cutting, while guaranteeing agood seal between the high-pressure zone and each low-pressure zone.Moreover, the pressure levels P1 and P0 are defined as a function of thedesired parameters for the cutting operation (taking into account thecomponent materials of the two wafer layers). In any case, theprogressive establishment of an overpressure P1 in the zone 21 aids thecutting operation by preventing any rupture of the layers 10 a and 10 b.

It is also possible to establish a control loop for controlling thepressure increase in zone 21 as a function of observed progress of theseparation front 100. This observation of the separation front can bemade, for example, by monitoring the optical characteristics of thesurface of the wafer, for example, by using visible and/or infraredlight. FIG. 1 a illustrates control loop 201, which receives input fromoptical monitoring device 203 concerning the progress of separation, andwhich controls valve 211 to supply zone 21 with controllable highpressure fluid.

FIGS. 2 a and 2 b illustrate a second alternative embodiment of theinvention. FIG. 2 a depicts the same wafer 10 subjected to attack by atleast one blade that includes a high-pressure fluid supply means. In theexample in FIG. 2 a, the wafer 10 is subjected to attack by two moveableblades 31 and 32 that are diametrically opposed to each other on eitherside of the wafer, in the same plane as the weakened interface 11.However, one of the blades can remain fixed and/or could include aholder for the wafer. This holder also would contribute to establishinga tight seal between the high pressure and low pressure zones by virtueof the seals that are attached on the two surfaces (the configurationand the role of the seals being explained below).

Each blade 31, 32 includes an internal supply conduit 310, 320 connectedto a high pressure fluid reservoir. A means is provided therein forcontrolling the establishment of a high pressure P1 in the conduit, andthe conduit opening is at the level of the leading edge of the blade. Inthis alternative embodiment, the establishment of a high pressure at thelevel of the interface ring is caused by injection of a fluid underpressure through the conduit of the blade after initiation of the attackof the wafer by the blade(s) (as shown by the position of the bladesshown in FIG. 2 b in which a seal is established between the high andlow pressure zones). In this embodiment, a high-pressure zone is createdat the interface ring, to attack the weakened interface and create ahigh pressure zone ahead of each blade so that the layer(s) of the waferare subjected to a pressure differential.

The embodiment of FIGS. 2 a and 2 b corresponds to a particularly simpleconfiguration for implementation of the invention, because thelow-pressure zones near the principal surfaces of the wafer correspondsimply to zones exposed to ambient atmospheric pressure (P0). It ishowever possible to expressly define the low-pressure zones with respectto the principal surfaces (or only one of the principal surfaces) of thewafer. For example, the wafer could be placed into a receptacle andseals could be used to define zones in the receptacle, so that the highpressure P1 is constantly provided by an internal conduit of the blade(or of the blades) that attack(s) the wafer. It is noted thatcomplementary means are also provided to assure a tight seal between thelow-pressure zones (in particular the zones arranged relative to theprincipal surfaces of the wafer) and the high pressure zones (inparticular the zones disposed ahead of the blades 31 and 32 at the timethe wafer is attacked by the blades, see FIG. 2 a). The complementarymeans can take the form, as in FIGS. 2 a and 2 b, of portions or partsof O-rings 3100 a, 3100 b, 3200 a and 3200 b. As shown more particularlyin FIG. 2 a, two seals 3100 a and 3100 b are thus affixed on the tworespective surfaces above and below the blade 31.

The blade has an overall geometry in the form of a half-ring (see FIG. 2b) whose inside diameter (the diameter of the central cavity of thehalf-ring) is less than the external diameter of the peripheral ring ofthe wafer by a distance corresponding to the desired depth of attack ofthe blade into the wafer. In this implementation, the two blades 31 and32 are identical and symmetrically arranged (as well as their respectiveO-rings), and the clamping of the two blades produces a ring thatattacks the wafer ring on its entire periphery by penetrating the waferonly to a desired depth. Each portion of the O-ring 3100 a, 3100 b thushas the shape of a half-ring that is fixed on it blade side in proximityto the leading edge of the blade. In particular, the distance betweenthe seal and the leading edge is defined so that when the blade attacksthe wafer the peripheral part of the respective layer 10 a and 10 barranged relative to the seal makes tight contact on the seal. Thus, aseal is created between the external environment of the wafer (exposedto the “low” atmospheric pressure P0, although this pressure could becontrolled in a sealed receptacle to have an entirely different value)and the zones of the wafer in which in which a desired high pressure isestablished (zones situated between the two layers 10 a and 10 b andahead of the leading edge of the blade).

It is noted that the blades 31 and 32 are identical and arrangedsymmetrically relative to the wafer as well as to their respective seals3100 a, 3100 b and 3200 a, 3200 b. It is also noted that, in terms ofclamping of the blades on the wafer, the ends of the seal 3100 a maketight contact with those of the seal 3200 a of the opposing blade insuch fashion as to create on the top of the blades an annular tightO-ring. The same also applies under the blade with regard to the seals3100 b and 3200 b. In this fashion, complete tightness or a completeseal is established between the low and the high pressure zones.

FIG. 2 b schematically illustrates the particular geometry of the blades31 and 32 which, in this embodiment, each have a half-ring shape whenviewed from above. In this case, the two blades 31 and 32 approach eachother until the rectilinear portions of their leading edges (theportions corresponding to a radius of the ring, the leading edge of eachblade between these two peripheral portions having a leading edge with acontour, when viewed from above, that corresponds to the contour of thecentral space of the half-ring) meet, and the cutting is then completed.

It is noted that it is not necessary for the blade to completelypenetrate the wafer surface. In fact, in the different alternativeembodiments of the invention, it is possible to carry out the cuttingoperation entirely by having the blade penetrate the wafer only to alimited depth and then to rely on the pressure differential (P1-P0) toperform cutting to finish separating the layers.

It is also important to note in FIG. 2 a the presence of two grippingelements 30 a and 30 b which contact the respective faces 10 a 1 and 10b 1 of the wafer. These gripping elements can include, for example,suction cups or suction means on their faces that are in contact withthe principal surface of the wafer. The gripping elements 30 a and 30 bcan thus aid in the separation of the layers 10 a and 10 b to facilitatecutting, and these gripping elements can be controlled by controllingthe distance from each other (so as to exert a traction force todirectly facilitate separation of the layers 10 a and 10 b). It is alsopossible to control the movement of these elements 30 a and 30 b in thedirection of the plane of the weakened interface 11, the two elementshaving displacements in the opposing directions in such a fashion as togenerate shearing forces to further facilitate cutting of the layers 10a and 10 b.

1. A device for cutting an assembly having two layers of material and aweakened interface there between, wherein the weakened interface definesan interface ring about the periphery of the assembly, comprising: ahousing adapted for accepting the assembly; at least one blade without afluid supply means for attacking the assembly at the interface ring; andat least one further element that cooperates with the blade andinterface ring to facilitate cutting of the assembly; wherein thefurther element comprises a first seal element for establishing ahigh-pressure zone between the housing and the assembly at the level ofthe interface ring, and for establishing a first low-pressure zone at afirst surface of the assembly; and a second seal element for furtherdefining the high pressure zone between the housing and the assembly,and for establishing a second low-pressure zone at a second surface ofthe assembly; wherein cutting is facilitated by controlling the pressurein at least one of the high pressure and the low pressure zones.
 2. Thedevice of claim 1 wherein the further element is at least one gripperfor applying a complementary mechanical action on at least one surfaceof the assembly.
 3. The device of claim 2, wherein the cutting comprisesapplying complementary mechanical action comprising at least one of atraction force perpendicular to the surfaces of the assembly and ashearing force oriented in the plane of the weakened interface.
 4. Thedevice of claim 1, wherein at least one of the first or second sealelements is an O-ring.
 5. The device of claim 1, wherein at least twoblades are provided and which further comprises an independenthigh-pressure supply for each blade of the device.
 6. The device ofclaim 1, which further comprises a control loop for controlling theincrease of high pressure in the high pressure zone as a function of theprogress of a separation front created during cutting.
 7. The device ofclaim 6, wherein the control loop is operatively associated with anoptical monitoring device that monitors the optical characteristics ofthe surface of the assembly using visible or infrared light.
 8. Thedevice of claim 1, wherein the high pressure zone is created byinjection of a fluid that has chemical properties enabling it to attackthe weakened interface and thus facilitate cutting.
 9. The device ofclaim 1, wherein the low-pressure zones are configured and adapted tofavor deformation of at least one of the layers of the assembly tofacilitate cutting.
 10. The device of claim 1, which further comprisesmeans for controlling the low pressure zones separately and differentlyto apply a pressure differential between the two layers, and thusprovide a greater load on one of the layers to facilitate cutting. 11.The device of claim 1, wherein the assembly has a generally circularperiphery and the blade has a concave crescent profile and a leadingedge that co-operates with an angular sector of the periphery of theassembly.
 12. The device of claim 1, wherein the first and second sealelements have sufficient elasticity to allow separation of the layers ofthe assembly from each other to facilitate completion of the cuttingwhile guaranteeing a good seal between the high pressure zone and eachlow-pressure zone.
 13. The device of claim 12, wherein the high pressurezone is created by injection of a fluid and the creation of anoverpressure in the high pressure zone aids cutting by preventingrupture of the layers of the assembly.
 14. A device for cutting anassembly having two layers of material and a weakened interface therebetween, wherein the weakened interface defines an interface ring aboutthe periphery of the assembly, comprising: a housing adapted foraccepting the assembly; at least one blade for attacking the assembly atthe interface ring; and at least one further element that cooperateswith the blade and interface ring to facilitate cutting of the assembly;wherein the further element comprises a first seal element forestablishing a high-pressure zone between the housing and the assemblyat the level of the interface ring, and for establishing a firstlow-pressure zone at a first surface of the assembly; and a second sealelement for further defining the high pressure zone between the housingand the assembly, and for establishing a second low-pressure zone at asecond surface of the assembly; means for controlling the low pressurezones separately and differently to apply a pressure differentialbetween the two layers, and thus provide a greater load on one of thelayers to facilitate cutting; wherein cutting is facilitated bycontrolling the pressure in at least one of the high pressure and thelow pressure zones.
 15. The device of claim 14 wherein the furtherelement is at least one gripper for applying a complementary mechanicalaction on at least one surface of the assembly.